This invention relates to digital magnetic recording, and more particularly to a magnetic recording disk drive where data is written while the magnetic recording layer is at an elevated temperature.
Magnetic recording disk drives store digital information by using a miniaturized thin film inductive write head. The write head is patterned on the trailing surface of a slider that also has an air-bearing surface (ABS) to allow the slider to ride on a thin film of air above the surface of the rotating disk. The write head is an inductive head with a thin film electrical coil located between the poles of a magnetic yoke. When write current is applied to the coil, the pole tips provide a localized magnetic field across a gap that magnetizes the recording layer on the disk into one of two distinct magnetic states (binary data bits).
The magnetic material for use as the recording layer on the disk is chosen to have sufficient coercivity such that the magnetized data bits are written precisely and retain their magnetization state until written over by new data bits. The data bits are written in a sequence of magnetization states to store binary information in the drive and the recorded information is read back with a use of a read head that senses the stray magnetic fields generated from the recorded data bits. Magnetoresistive (MR) read heads include those based on anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), such as the spin-valve type of GMR head, and the more recently described magnetic tunnel junction (MTJ) effect. Both the write and read heads are kept in close proximity to the disk surface by the slider""s ABS, which is designed so that the slider xe2x80x9cfliesxe2x80x9d over the disk surface as the disk rotates beneath the slider. As the recording bit size decreases to increase the data density on the disk, several problems arise with the conventional thin film inductive write head and writing process.
The first problem relates to the xe2x80x9csuperparamagneticxe2x80x9d effect. The areal data density (the number of bits that can be recorded on a unit surface area of the disk) of magnetic disk drives is now approaching the point where the data bits are so small they can be demagnetized simply from thermal agitation within the magnetized bit (the so called the xe2x80x9csuperparamagneticxe2x80x9d effect). The conventional approach to circumventing this problem is to increase the magnetic anisotropy and coercivity of the magnetic material in the recording layer on the disk to improve the thermal stability. However, this requires that the write head be made with a material with high saturation moment to increase the write field of the head so the head can write on the high coercivity media. Based on the properties of known materials, the ultimate write field of the head can only be increased by about 30%, thus severely limiting future data density growth. In addition, the increased data rate required at higher areal density requires that the magnetic properties of the materials used in the write head have to be optimized, which is very difficult to achieve if the materials suitable for use are limited to only those that have a very high saturation moment.
The second problem relates to the need for narrow track widths to increase the areal data density. As the track width gets narrower, the portion of the track width that is defined by the track edge stray or fringe fields from the write head becomes a larger portion of the track width since the spacing between the head and disk cannot be scaled due to engineering difficulties with head and disk tribology. This degrades the data quality since more and more of the written track width consists of the poorly written edge regions. In addition, to reduce the track width while still providing an adequate write field requires that one of the pole tips of the write head has a geometry in which the height of the pole is much greater than its width. A write head with such a high aspect ratio pole tip geometry is difficult to fabricate.
Since it is known that the coercivity of the magnetic media (i.e., the magnetic recording layer on the disk) is temperature dependent, one proposed solution is xe2x80x9cthermally assistedxe2x80x9d magnetic recording (TAMR), wherein the magnetic material in the media is heated locally to near or above its Curie temperature during writing so that the coercivity is low enough for writing to occur, but high enough for thermal stability of the recorded bits at ambient temperature. Several approaches to TAMR have been proposed, including use of a laser beam or ultraviolet lamp to do the localized heating, as described in IBM Technical Disclosure Bulletin, Vol. 40, No. 10, October 1997, pp. 65-66, and IBM""s U.S. Pat. No. 5,583,727. In these approaches, the heating area is typically wider than the data bit so that the data bit dimension is still determined by the size of the write head. Thus while the first problem described above is addressed by these TAMR approaches, the second problem is not addressed because the write head geometry and fringe fields still limit the reduction in track width that can be achieved.
A read/write head for use in a magneto-optic (MO) or TAMR system is described in U.S. Pat. No. 5,986,978, wherein a special optical channel is fabricated adjacent to the pole or within the gap of a write head for thermally assisted writing of the MO or magnetic media by directing laser light or heat down the channel. An older technology unrelated to TAMR is also known for use in a copy machine which magnetizes a film with an image that is then transferred to a paper using magnetic ink. In that technology, as described in U.S. Pat. No. 4,520,409, a ring type head uses a resistive heater in the gap between the poles to modulate heat pulses to the film while the pole piece applies a constant bias field to the film.
What is needed is a write head for a TAMR system that allows for narrow track widths to be achieved without the constraint that the track width is determined by the geometry of the write head pole tips or the fringe fields from the write head.
The invention is a thermally-assisted magnetic recording disk drive wherein the thin film inductive write head includes an electrically resistive heater located in the write gap between the pole tips of the write head. The resistive heater is sandwiched between first and second spacer layers that are located between the pole tips of the write head. In one embodiment, referred to as current-perpendicular-to-the plane (CPP), the spacer layers are electrically conductive and the pole tips serve as the electrical leads to provide electrical current in a direction generally perpendicular to the layer of resistive heater material. In a second embodiment, referred to as current-in-the plane (CIP), the spacer layers are formed of insulating material and electrical leads are formed as portions of a film between the spacer layers and in contact with each side of the resistive heater. The width of the resistive heater is less than the width of the pole tips. Thus since only the region of the magnetic layer on the disk that is heated by the resistive heater can be written by the pole tips of the write head, the data track width on the disk is defined by the width of the resistive heater, not by the geometry of write head pole tips.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.